This invention relates to a floating-probe flowmeter for measuring the flow of a moving medium, with a measuring tube through which the medium travels against the force of gravity and which measuring tube contains a float that is capable of moving at least in the direction of the flow.
1. Field of the Invention
Floating-probe flowmeters of the type referred to above have for years been used for determining volume flow rates through closed pipelines, and due to their simplicity and ruggedness they have met with broad appeal especially in the chemical industry and in process engineering but also in the realm of medicine and the natural sciences. In its simplest implementation, a conventional floating-probe flowmeter consists of a flared measuring tube and a float that is suitably designed as a probe capable of moving freely at least in the direction of the flow. The medium whose flow rate is to be measured flows against the force of gravity, i.e. essentially in an upward direction.
The combination of measuring tube and float thus constitutes a throttle-type flow regulator. The density of the float is greater than that of the medium flowing through the measuring tube. As a function of the flow rate the float, once settled, is suspended at a particular level within the measuring tube, which level is determined by the equilibrium between the hydrodynamic force generated by the flow and transferred to the float and the differential force between the weight and the buoyancy of the float. That suspended position of the float, also referred to as its lift, is read out by the observer either directly off a scale on a transparent measuring tube, or it is signaled via a coupling device such as a magnetic coupling to an external gauge and/or to an electrical transducer.
Apart from the volume flow it is also the viscosity of the moving medium that plays a significant role in determining the lift of the float. It follows that the floating-probe flowmeter will always have to be calibrated for a particular medium of a specific predefined viscosity. But it also means that whenever the viscosity of a flowing medium fluctuates or another medium with a different viscosity is measured, the floating-probe flowmeter will no longer work properly, i.e. it usually fails to provide the correct volume flow readings.
Specifically, too, the viscosity of the flowing medium produces a boundary layer on the surface of the float facing the flow of the medium. At the interface of that boundary layer the float is exposed to shearing and friction forces that significantly affect the lift of the float.
2. Description of the Prior Art
In an effort to at least reduce the effect of viscosity on the lift of the float, the floats of conventional floating-probe flowmeters have frequently been provided with a spoiler-type flow-breaking edge intended to deflect the flow away from the surface of the float, again to at least diminish the effect of the viscosity on the lift of the float. Solutions of that nature by means of a breaking edge have some functional merit, but the attainable reduction in the formation of a boundary layer is minor, generally making it unavoidable that behind the breaking edge the flow reconverges to hug the float, thus forming a new boundary layer. Finally, viscosity-related effects on the inner surface of the measuring tube also appear to affect the lift of the float.
It is, therefore, the objective of this invention to introduce a floating-probe flowmeter in which the lift of the float remains essentially unaffected by the viscosity of the flowing medium.
In a floating-probe flowmeter as described above, this objective is achieved in that at least the surface of the float that is exposed to the flow of the medium is provided with a microstructure and/or that the inner surface of the measuring tube at least in the area of float movement is provided with a microstructure.
This means that, according to the invention, the surface of the float that is exposed to the flow of the medium and/or the inner surface of the measuring tube should not be xe2x80x9csmoothxe2x80x9d in the traditional sense but should intentionally be given a certain textured roughness in the micron range. Such texture can be obtained for instance by providing the surface of the float that is exposed to the flow of the medium and/or the inner surface of the measuring tube with a xe2x80x9cpeak-and-valleyxe2x80x9d microstructure with numerous peaks separated by corresponding valleys.
Preferably, the peaks of the microstructure are between 5 and 400 xcexcm and ideally between 5 and 100 xcexcm high, while the apex-to-apex distance between neighboring peaks is between 5 and 800 xcexcm and ideally between 5 and 200 xcexcm. In this case, the height and spacing of the peaks across the entire surface of the float that is exposed to the flow of the medium and across the entire inner surface of the measuring tube may be anywhere within the ranges indicated so that these surfaces may feature very low and very high peaks with very small as well as very large spaces between these peaks. In a preferred embodiment of the invention, however, neighboring peaks are roughly identical in height while the interapical distance between neighboring peaks measures about 1 to 2 times the height of the peaks.
The float may consist of practically any material. In a preferred embodiment of the invention, however, the peaks of the microstructure are rendered hydrophobic. A float with a microstructure of hydrophobic peaks ensures not only the aforementioned avoidance of the formation of a boundary layer and thus an avoidance, or at least a reduction of the effect, of the flowing medium""s viscosity on the lift of the float, but also a certain cleaning action, i.e. contaminants carried by the medium and adhering to the float are easily removed from the hydrophobic surface by the constant scavenging action of the medium.
This cleansing effect can also be utilized on all other surfaces of the floating-probe flowmeter that make contact with the flowing medium, most particularly the inner surface of the measuring tube at least in the area of movement of the float. Therefore, in a preferred embodiment of the invention, the inner surface of the measuring tube at least in the area of movement of the float is provided with a microstructure of hydrophobic peaks for producing the aforementioned cleansing effect.
There are numerous ways in which the floating-probe flowmeter according to this invention can be configured and further enhanced. In that context, attention is invited to the dependent claims and to the following detailed description of preferred embodiments of the invention with reference to the attached drawings.